In the medical, pharmaceutical and biological fields as well as the food and beverage industries, including those involving manufacturing, research, clinical testing and processing, fluids are commonly tested or filtered which contain proteinaceous materials. Many of the media used in diagnostic testing or filtration provide adequate performance with respect to retention of materials sought to be retained, such as solid or gelatinous materials, including biological organisms, cell debris and other particulate matter. Commonly, such media used for filtering proteinaceous material-containing fluids also provide rapid flow rates when initially placed in service by virtue of low pressure drops across the membranes. Many of these materials, such as cellulose esters, however, exhibit poor hydrolytic stability and tend to decompose slowly when subjected to continuous use and particularly when exposed to conditions of steam sterilization. There is a tendency by some media, particularly cellulose esters such as cellulose acetate and cellulose nitrate, to decompose as a result of prolonged exposure to solvents or biological materials. In addition, some of these materials tend to be brittle and cellulose nitrate is flammable.
Other media, such as polyamides, particularly nylon, exhibit generally good hydrolytic stability, relatively low flammability and desirable physical properties, such as high strength and flexibility. The polyamides, particularly nylon 66, demonstrate high retention of materials sought to be retained, usually resulting from precise manufacturing control of absolute pore ratings. In many applications, polyamide media are employed in the form of membranes which exhibit low pressure drops across the membrane. However, when such applications involve filtration or passage of solutions containing proteinaceous materials, the pressure differentials across the filtration media frequently increase during use because continued contact of such membranes with proteinaceous materials results in the pores of the membrane being plugged with sorbed proteinaceous material and performance thereby is adversely affected. In many instances, the blockage is irreversible and a costly membrane must be discarded. Thus, a membrane which in most respects is quite suitable for the intended purpose is rendered useless by an undesirable adsorption of proteinaceous material. In some instances, the retained protein may be desired but is rendered unusable and may, therefore, represent a costly loss.
Certain filtration media also tend to adsorb from solutions certain non-proteinaceous adjuvants, such as color and flavor agents in foods and beverages, polyphenols in beer, and certain preservatives in pharmaceutical preparations. Thus, although nylon possesses many of the positive properties enumerated above which make it an excellent material for applications in which a liquid is to pass through the pores of the material (for example in filtration or diagnostic applications), it is also a material which demonstrates an affinity not only for proteinaceous materials but also for certain color agents, polyphenols and polar preservatives. Thus, even if the sorption of proteinaceous material were overcome, nylon filtration media would still possess the drawback of having a strong affinity for the aforementioned adjuvants.